When I rang the support line, the very helpful support worker explained that I should put more pressure on the clip on the pad-insert, and I finally lucked on the insight that I had to press the little lever on the clip AND ALSO press my thumbnail on the almost invisible join between the clip and the tape.
I'm rather surprised that the difficulty I had in undoing the clip hasn't led to other complaints, because I really had tried several times before I gave up and rang the support line. So I would recommend this product but I'd explain how to open the clip as part of my recommendation.